Freezing, progressive applications

Fractional solidification and its applications to obtaining ultrapure chemical substances, has been treated in detail in Fractional Solidification by M.Zief and W.R.Wilcox eds, Edward Arnold Inc, London 1967, and Purification of Inorganic and Organic Materials by M.Zief, Marcel Dekker Inc, New York 1969. These monographs should be consulted for discussion of the basic principles of solid-liquid processes such as zone melting, progressive freezing and column crystallisation, laboratory apparatus and industrial scale equipment, and examples of applications. These include the removal of cyclohexane from benzene, and the purification of aromatic amines, dienes and naphthalene. 

There has been a demand for the development of cryopreservation methods for plant cells to avoid the troublesome maintenance of tissue cultures and the danger of microbial contamination. The most successful method for cryopreservation of plant cells reported so far has been the freezing of callus cultures or shoot tips [36, 37]. As the system here enables us to obtain sufficient initial shoot materials, its potential practical application to cryopreservation is in progress. In addition, the system of adventitious shoot formation might be a promising tool to investigate relationship between morphogenesis (shoot formation) and alkaloid biosynthesis. 

One of the most active areas of research in the statistical mechanics of interfacial systems in recent years has been the problem of freezing. The principal source of progress in this field has been the application of the classical density-functional theories (for a review of the fundamentals in these methods, see, for example, Evans ). For atomic fluids, such apphcations were pioneered by Ramakrishnan and Yussouff and subsequently by Haymet and Oxtoby and others (see, for example, Baret et al. ). Of course, such theories can also be applied to the vapor-liquid interface as well as to problems such as phase transitions in liquid crystals. Density-functional theories for these latter systems have not so far involved use of interaction site models for the intermolecular forces. 

In the years that have passed, a remarkable progress on both technical and physical aspects of freeze-drying was performed, and safe and reproducible methods required for industrial application have been established. 

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